The invention relates to the field of intravascular delivery systems, and more particularly to dilatation balloon catheters.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guide wire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guide wire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy, over the previously introduced guide wire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion.
In the design of catheter balloons, balloon characteristics such as strength, flexibility and compliance must be tailored to provide optimal performance for a particular application. An important consideration in the design of the dilatation catheter assemblies is the flexibility of the distal tip of the catheter at the distal end of the balloon while maintaining the strength of the bond between the catheter and the balloon material. This flexibility affects the ability of the catheter for negotiating through the patient""s vasculature without causing injury thereto.
Therefore, what has been needed is a dilatation balloon catheter with a flexible tip and while maintaining the integrity of the bond between the catheter and the balloon. The present invention satisfies these and other needs.
The invention is directed to a catheter assembly. The catheter includes an elongated shaft having proximal and distal sections, and further includes an inflatable balloon on a portion of the distal shaft section and in surrounding relation thereto. The balloon has proximal and distal tapered regions and an intermediate region longitudinally disposed therebetween. The proximal and distal tapered regions each has a first end adjacent the intermediate region and a second end opposite the first end. The wall thickness of the proximal and distal tapered regions, may, increase from the first end to the second end. A fluid-tight bond is formed between the catheter shaft and at least a section of at least one of the proximal and distal tapered regions at the second end thereof. The bond is preferably a fusion bond. At least a portion of the either or both the proximal and distal tapered regions in the bond interface is at least partially crystalline. Preferably, the crystallinity at the interface is greater than the crystallinity of the starting material from which the balloon is formed.
In an alternate embodiment, the assembly further includes an atraumatic distal tip with a distal end disposed at least substantially coaxial with the distal shaft section and extends distally from the second end of the balloon. A bond is formed between the catheter shaft and the second end of the balloon.
In another embodiment, a cylindrical collar is disposed at least partially about the atraumatic distal tip and at least partially about tip portion of the distal catheter shaft. The collar forms a distal bond with at least a section of the distal tapered region at the second end thereof.
The balloon, atraumatic distal tip, and the collar are formed, at least in part, from a material independently selected from the group consisting of copolyamides, polyurethane, and copolyesters.
The invention is also directed to a method for forming the catheter assembly of the present invention. By way of manufacture, an elongated shaft having proximal and distal sections and a distal tip is provided. An inflatable balloon is disposed on a portion of the distal shaft section in surrounding relation thereto. The balloon has proximal and distal tapered regions and a intermediate region longitudinally disposed therebetween. The proximal and distal tapered regions each has a first end adjacent the intermediate region and a second end opposite the first end. Furthermore, the balloon has proximal and distal shaft regions adjacent the second end of the proximal and distal tapered regions, respectively. The proximal and distal shaft regions extend away from the first end of the corresponding proximal and distal tapered regions.
The balloon distal shaft region at the second end of the distal tapered region is removed such that the balloon material at least substantially terminates at the second end of the tapered region. A protective sleeve is provided at the balloon distal tapered region. The protective sleeve covers, at least in part, the second end of the balloon tapered region and the shaft distal tip.
A substantially monochromatic energy at a wave length of maximum spectral absorption of the materials forming the balloon and the distal section of the catheter shaft is controllably directed onto the distal catheter shaft and at least a section of the distal tapered region at the second end thereof to concentrate the monochromatic energy to form a bond site between the distal catheter shaft and the at least a section of the distal tapered region. At least a portion of the materials forming the distal catheter shaft and the balloon along the bond site and the region immediately adjacent thereto is melted. The melted material is then allowed to cool and solidify to form a fusion bond between the distal catheter shaft and the balloon. The protective sleeve is then removed.